The unicellular flagellate, Euglena, will be used as a model membrane system in which flagellar membranes can be biochemically and developmentally analyzed separately from the cell surface membrane. Through iodination with I125 external membrane components are tagged and will be subsequently followed in regenerating cells. Isolated membranes from flagellar and flagellar-free surfaces can be isolated and specific glycoproteins purified for constructing antibody probes. These will be used for identifying regional differences in membrane antigen distribution under a variety of experimental conditions. The nature of glycoprotein attachment to axonemal microtubules is also being examined through the use of radiolabeled peptide fragments of flagellar mastigonemes and through reciprocal experiments using radiolabeled axonemal components and intact mastigonemes.